Summer air pollution is easy to see in the haze of wildfire smoke. But dangerous levels of some air pollutants, such as ozone, can be invisible. That’s why it’s important to pay attention to the Air Quality Index (AQI), which can help you determine when to take precautions to prevent negative health effects.

A healthy adult who is exposed to air pollutants for a short time or at a low dose may not have long-term problems. But children and older adults are more vulnerable to health effects from air pollution. And for people with a heart or respiratory condition, even a small dose or a short exposure can make symptoms worse. Longer exposure or a higher dose can lead to serious illness or death.

• The AQI is based on Environmental Protection Agency (EPA) tracking of air pollutants that cause major health effects:
• Ground-level ozone
• Particle pollution (also known as particulate matter)
• Carbon monoxide
• Sulfur dioxide
• Nitrogen dioxide

Air quality is reported on a color-coded scale that ranges from 0 to 500. The higher the AQI value, the greater the health concern due to increased pollution:

• Green (0-50): Good
• Yellow (51-100): Moderate
• Orange (101-150): Unhealthy for Sensitive Groups
• Red (151-200): Unhealthy
• Purple (201-300): Very Unhealthy
• Maroon (301 and higher): Hazardous

Officials issue an air quality alert for sensitive groups when the AQI exceeds 100. Levels higher than 300 are very hazardous for everyone.

The National Weather Service suggests taking the following actions to guard your health when air quality alerts are in effect:

• Stay informed about air quality conditions in your area. You can look up air quality by zip code or city and state at AirNow.gov.
• Choose a less strenuous activity.
• Shorten outdoor activity and take more breaks.
• Reschedule activities.
• Move your activity inside.

For specific precautions, see Airnow.gov’s activity guides. These one-page summaries list ways to protect your health when ozone pollution and particle pollution reach unhealthy levels for sensitive groups, people with asthma and everyone else. A guide for schools also lists ways to keep children active while protecting their health.